This invention relates to electrical transmission lines and more particularly to woven cables having a plurality of conductors for use in transmitting high frequency electrical signals. Multiconductor transmission cables are commonly used such as in the connection of peripheral equipment to a central computer complex for transmitting input and output data signals.
Use of high frequency transmission cables in sophisticated information and communication systems necessitates that the characteristic impedance of the cable be accurately controlled. Unmatched impedances can result in signal errors which represent erroneous data in the system. Another problem commonly had in high frequency multi-conductor cables is the occurrence of cross-talk interference between adjacent signals owing to the close proximity and sensitivity of the wires in a side-by-side pattern. Quite often a cross-talk interference signal of two to four percent of the signal line voltage can be induced in an adjacent signal line which may falsely trigger a logic circuit.
Various multiconductor cable configurations are known. These can be broadly classified into a first group comprising a plurality of substantially parallel conductor wires embedded in a dielectric material such as shown in United States Letters Pat. No. 3,818,117 and a second group wherein a plurality of conductor wires are arranged in a side-by-side relationship and interwoven with insulating fiber strands to form a woven cable such as shown in United States Letters Pat. No. 3,447,120. Both of these patents utilize the concept of a "shared" ground line or wire wherein adjacent signal wires share a common ground wire therebetween.
The characteristic impedance of such a cable is controlled by the geometrical configuration of the signal and ground wire relationship. Likewise, cross-talk may be controlled by spacing between the signal wires. In the case of a woven cable, the "shared" ground wire concept requires that the signal and ground wires have substantially equilateral or symmetrical spacing therebetween for matched impedance. If the spacing between signal wires is altered to reduce cross-talk interference, the resulting dissymetry between the signal wires and the shared ground wires creates unmatched impedances between signals. Such a concept does not allow for versatility in the geometrical configuration of the cable.